1. Technical Field
The invention relates to a sliding element in an internal combustion engine, in particular a piston ring.
2. Related Art
Fuel consumption plays a significant role in the reduction of carbon dioxide emissions from internal combustion engines. It is greatly affected by the frictional losses in the engine, especially in the area of the pistons, such as at the piston rings. There is consequently a demand for sliding elements in internal combustion engines, in particular piston rings, that exhibit as favourable as possible a frictional performance throughout their service life. With regard to the overall service life, it is necessary to specifically consider the running-in performance, a possible lack of lubrication, and potential scorching, all of which result in altered tribological characteristics.
In the above-mentioned field, PVD coatings of hard materials are known which have a good wear resistance, but which could be improved with regard to their coefficients of friction.
DE 10 2005 063 123 B3 discloses a layer structure comprising, from the outside inwards, a running-in layer, an adhesive layer, and a wear-protection layer. However, it has become apparent that further improvements can be made to the performance of the friction characteristics over its service life.
U.S. Pat. No. 6,528,115 relates to a sliding element with a carbon coating having a varying sp2/sp3 ratio, particularly one which may decrease outwardly from the substrate, and then increase again to the outside of the coating.